For those many tobacco smokers who cannot or will not give up smoking, there are a number of devices which are effective, in some degree, in removing harmful tars, carbon monoxide and nicotine constituents from smoke. There are "filter tips" which are fixed to an end of a cigarette during manufacture. Each cigarette has its individual filter. The constraints in the area of manufacturing technique and cost faced by the designers of such filters are very formidable. They work, but usually not very well, and with little uniformity.
Far less constraint is placed on the designer of the reusable filter that can be cleaned and used over and over. The most effective of these cigarette holder-type filters combines an air inlet that opens to a mixing chamber just downstream from the cigarette end. The smoke is cooled in that chamber by being mixed with air. The more dense components, tar and nicotine materials, begin to condense to liquid and semi-liquid form.
The mixing chamber is defined by a barrier in the smoke path which is formed with an opening at which the smoke and its condensates are accelerated. Thereafter, the smoke and condensates are made to flow through a labyrinth where the condensates are made to adhere to the labyrinth wall while the smoke continues on to the bit end as the smoke inhales. The air inlet-mixing chamber-barrier part of the design is predictable, but downstream labyrinth design has proven to be anything but predictable.
The labyrinth section must meet two basic requirements. Most of the condensates must adhere to the labyrinth wall, and the cost must be low. A number of labyrinth designs which meet those requirements have been discovered. Those that have been most successful permit the removal of different degrees of tar and nicotine by changing the size of the air inlet opening to the mixing chamber and require no change in the labyrinth structure. To change air inlet opening size, it is common to market the holders in sets--each one of the set having an inlet of different size.
Holders of that type have been produced in very effective form. The several holders of a set typically remove from fifty to ninety percent of the tar and nicotine materials that would reach the user in the absence of a filter. Moreover, a large proportion of the carbon monoxide is entrained in the condensate and is removed with it. However, the most effective filter does nothing for the smoker who will not use it.
The primary reasons, it appears, why many smokers will not use, or abandon the use of, those holder-type filters is that they are too big for attractiveness, or too difficult to attach, or too messy to clean. While the problem is solved in many holder type filters, many smokers want the trapped, bad material to be relatively invisible, although discernable, so that they can know that the filter is being efficient.
Despite the number and variety of cigarette filtering devices, there is still a need, not for more effective filters, but for an effective filter that larger numbers of smokers will accept.